A teenage girl's decision to have an abortion depends much more on factors such as the availability of family planning clinics and female GPs in their area than her own moral preferences, according to a new survey.

The Joseph Rowntree Foundation, a social policy charity, will publish a report next week that shows abortion rates for 15 to 17-year-old girls vary wildly across the country and are largely determined by socio-economic events. Ellie Lee, who conducted the two-and-a-half-year study for the Centre for Sexual Health Research at the University of Southampton, said: 'The proportion of abortions has increased. What we were more interested in was why rates vary so much across the country.'

Just under half of all 15 to 17-year-old pregnancies were terminated last year, a total of 15,750 in England and Wales, according to government statistics, but in Derwentside, Co Durham, the figure was just 18 per cent. In contrast, 76 per cent of pregnant 15 to 17-year-olds in Eden, Cumbria, decided on termination. 'Service across the country is patchy,' said Ellie Lee, who conducted the 30-month study for Southampton University's Centre for Sexual Health Research.

The study, in which 103 teenage girls were interviewed, examined the link between social background and attitude to abortion. Researchers found that more deprived areas have both higher conception rates and a lower proportion of teenage pregnancies being aborted.

They concluded: 'Those opting for abortion tend to have high expectations of life and clear pathways marked out for the future.' As one middle-class girl put it: 'There was no question of me keeping it because I knew I was going to university.'

In contrast, girls who continued with pregnancy perceived motherhood in a positive light. 'It's the best thing that ever happened to me ... If I hadn't had the baby, I would've been in jail,' said one.

'As long as poverty stays the way it is, young women in deprived areas will have babies,' said Lee. 'There is no point having a go at them and saying, "It will ruin your life," because having a baby gives them a sense they have a future.'

The study showed termination levels were influenced by a range of independent factors: the quality and availability of family planning clinics, the proportion of female GPs and the availability of private abortion clinics. It also found that some abortion services are struggling to meet demand. In a small number of cases, waiting times are longer than the government's recommended three weeks.

Significantly, researchers found that some clinicians are reluctant to abort beyond three months of pregnancy, and some teenagers have to travel greater distances for a termination, something that may help to explain the acute geographical differences in abortion rates.